Railway Tunnel No. 1 of the Sierra Greenway Nature Trail. This tunnel crosses an outcrop of sandstone and marl to maintain the gradient of the railway line. This outcrop will be crossed by the following four tunnels. It is 170 meters long and is equipped with lighting; however, a flashlight is recommended.
The tunnels in this railway section were constructed using shoring (supporting the excavation) with wooden beams and props, followed by formwork for the concrete slab that supports the tunnel. The tunnel entrance is finished with hewn limestone from a quarry located opposite Zaframagón.